EP3929500B1

EP3929500B1 - Air conditioner control method and device, and air conditioner

Info

Publication number: EP3929500B1
Application number: EP19922216.7A
Authority: EP
Inventors: Dashu ZOU
Original assignee: Midea Group Co Ltd; GD Midea Air Conditioning Equipment Co Ltd
Current assignee: Midea Group Co Ltd; GD Midea Air Conditioning Equipment Co Ltd
Priority date: 2019-03-25
Filing date: 2019-07-29
Publication date: 2023-05-17
Anticipated expiration: 2039-07-29
Also published as: CA3134876A1; EP3929500A1; US20220010979A1; EP3929500A4; CA3134876C; ES2948266T3; WO2020191976A1

Description

FIELD

The present invention relates to the technical field of electrical appliances, and more particularly, to a control method for an air conditioner, a control device for an air conditioner, and an air conditioner.

BACKGROUND

For air conditioners in related technologies, an electric control box is usually subjected to heat dissipation via air cooling. However, the heat dissipation effect is poor at a high temperature, and the heat generated by the electric control box cannot be taken away timely to reduce the temperature of components, thereby affecting the service life and reliability of the air conditioner. Meanwhile, a variable frequency air conditioner cannot reach high operating frequencies at high temperatures, and thus cannot display advantages of the variable frequency air conditioner to meet user requirements.
Patent application publication JP2014102050A discloses a refrigeration device including a device cooler for cooling a plurality of power devices by a refrigerant flowing in a refrigerant circuit, to suppress dew condensation on a power device corresponding to a stopped apparatus among the plurality of power devices.

SUMMARY

The present invention is to at least solve one of technical problems existing in the related art. Aspects of the present invention are set out in the accompanying claims.
A control method according to the invention is defined in claim 4. A controller according to the invention is defined in claim 5. Further preferred embodiments are defined in the dependent claims 1-3.

DESCRIPTION OF DRAWINGS

Fig. 1 is a schematic diagram illustrating structure of an air conditioner not according to the present invention;
Fig. 2 is a schematic diagram illustrating structure of an air conditioner according to the present invention;
Fig. 3 is a flow chart showing a control method for an air conditioner according to the present invention;
Fig. 4 is a schematic diagram illustrating structure of a control device for an air conditioner according to the present invention;

DETAILED DESCRIPTION

Reference will be made in detail to embodiments of the present invention. The same or similar elements and the elements having same or similar functions are denoted by like reference numerals throughout the descriptions. The embodiments described herein with reference to drawings are illustrative, and used to generally understand the present invention. The embodiments shall not be construed to limit the present disclosure.
A control method for an air conditioner, a control device for an air conditioner and an air conditioner in embodiments of the present disclosure are described with reference to the drawings.
Fig. 1 is a schematic diagram illustrating structure of an air conditioner not according to the present invention.
A shown in Fig. 1, the air conditioner includes: an outdoor condenser 11, an indoor evaporator 12, a first electronic expansion valve 15, a throttle valve 16, and a heat dissipation coolant pipe 14 arranged in an electric control box 13, in which

the outdoor condenser 11 is communicated with a first end of the heat dissipation coolant pipe 14 via the first electronic expansion valve 15,
the indoor evaporator 12 is communicated with a second end of the heat dissipation coolant pipe 14 via the throttle valve 16,
the first electronic expansion valve 15 is configured to throttle a coolant in a heating mode, and
the throttle valve 16 is configured to throttle the coolant in a cooling mode.

Among them, the heat dissipation coolant pipe 14 may be a section of specific coolant pipe arranged in the electric control box 13.
The outdoor condenser 11 is communicated with a first end of the heat dissipation coolant pipe 14 via the first electronic expansion valve 15, the indoor evaporator 12 is communicated with a second end of the heat dissipation coolant pipe 14 via the throttle valve 16, and the heat dissipation coolant pipe 14 is arranged in an electric control box 13. The heat dissipation coolant pipe 14 is configured to dissipate heat from the electric control box 13, thereby timely removing heat generated by the electric control box 13 under a high temperature, lowering the element temperature, and improving the reliability and service life of the air conditioner. Further, the invention enables a variable frequency air conditioner to reach high operating frequencies and output high power under a high temperature, thereby displaying advantages of the variable frequency air conditioner and meeting user requirements.
Among them, the throttle valve 16 may specifically be a one-way throttle valve. In the heating mode, the first electronic expansion valve 15 is configured to throttle a coolant. In the cooling mode, the throttle valve 16 is configured to throttle the coolant in one direction. Therefore, condensation in the electric control box 13 can be avoided, thereby increasing the reliability of the electric control box 13.
According to the air conditioner, the outdoor condenser is communicated with a first end of the heat dissipation coolant pipe via the first electronic expansion valve, the indoor evaporator is communicated with a second end of the heat dissipation coolant pipe via the throttle valve, and the heat dissipation coolant pipe is arranged in an electric control box. The heat dissipation coolant pipe is configured to dissipate heat from the electric control box of the air conditioner, thereby timely removing heat generated by the electric control box, lowering the element temperature, and improving the reliability and service life of the air conditioner. Further, the invention enables a variable frequency air conditioner to reach high operating frequencies and output high power under a high temperature, thereby displaying advantages of the variable frequency air conditioner and meeting user requirements.
Fig. 2 is a schematic diagram illustrating structure of an air conditioner according to the present invention.
As shown in Fig. 2, based on the embodiments shown in Fig. 1, the air conditioner further includes a compressor 17, a second electronic expansion valve 18 and a plate heat exchanger 19, in which the indoor evaporator 12 is communicated with the throttle valve 16 via a first coolant branch of the plate heat exchanger 19, the compressor 17 is communicated with the throttle valve 16 via a second coolant branch of the plate heat exchanger 19 and the second electronic expansion valve 18 in sequence, and the second electronic expansion valve 18 is configured to throttle the coolant in a heating mode.
In embodiments of the present disclosure, the compressor 17 may specifically be a compressor with air-injection enthalpy-increasing as shown in Fig. 2. The compressor 17 may include a compressor exhaust port 35, a compressor air return port 33, and a compressor air-injection enthalpy-increasing port 34. An exhaust temperature sensor 30 may be arranged at outside of an exhaust pipe of the compressor 17 and is configured to detect the exhaust temperature of the compressor 17. The air conditioner may also include a high-pressure switch 29 and a low-pressure switch 32. One end of the high-pressure switch 29 is embedded inside the exhaust pipe of the compressor 17, which is configured to detect the exhaust pressure and realize system protection when the pressure is higher than its cut-off value. One end of the low-pressure switch 32 is embedded inside the return air pipe of the compressor 17, which is configured to detect the return air pressure and realize system protection when the pressure is lower than its cut-off value.
The plate heat exchanger 19 is configured to, in the heating mode, realize heat exchange of coolants with different temperatures in the first coolant branch and the second coolant branch passing through the inside of plate heat exchanger 19, so as to make the coolant in the compressor air-injection enthalpy-increasing port 34 to be gaseous, thereby greatly increasing the heating capacity output of the compressor 17 under certain conditions. Among them, an air-injection enthalpy-increasing inlet temperature sensor 27 and an air-injection enthalpy-increasing outlet temperature sensor 28 are respectively arranged at air-injection enthalpy-increasing inlet and air-injection enthalpy-increasing outlet of the air-injection enthalpy-increasing pipeline (the second coolant branch) of the plate heat exchanger 19 and are configured to respectively detect the temperatures at the air-injection enthalpy-increasing inlet and the air-injection enthalpy-increasing outlet. The second electronic expansion valve 18 is configured to throttle the coolant in the heating mode, which can be specifically operated according to the temperature at the air-injection enthalpy-increasing inlet and the temperature at the air-injection enthalpy-increasing outlet.
As shown in Fig. 2, based on the embodiments of Fig. 1, the air conditioner further includes a four-way valve 20 and a liquid storage tank 21.
A first valve port of the four-way valve 20 is communicated with the outdoor condenser 11. A second valve port of the four-way valve 20 is communicated with the indoor evaporator 12. A third valve port of the four-way valve 20 is communicated with the liquid storage tank 21. A fourth valve port of the four-way valve 20 is communicated with the compressor 17. The liquid storage tank 21 is communicated with the compressor 17.
As shown in Fig. 2, based on embodiments of Fig. 1, the air conditioner further includes a separator 22, in which the liquid storage tank 21 and the compressor 17 are respectively communicated with the fourth valve port of the four-way valve 20 via the separator 22.
In embodiments of the present disclosure, the air conditioner may further include an oil return capillary 31. The separator 22 is configured to separate cold refining oil discharged from the compressor. The discharged cold refining oil is returned to the compressor 17 by passing through the oil return capillary 31 and the return air pipe of the compressor under the action of the difference of high pressure and low pressure, so as to avoid the compressor 17 being oil shortage.
As shown in Fig. 2, the air conditioner may further include an outdoor ambient temperature sensor 23, a condenser middle-region temperature sensor 24, an indoor ambient temperature sensor 25, and an evaporator middle-region temperature sensor 26. Among them, the condenser middle-region temperature sensor 24 is arranged at a surface of a copper pipe located at a middle region of the outdoor condenser 11 and configured to detect a temperature of the middle region of the outdoor condenser. The outdoor ambient temperature sensor 23 is arranged at a fin on the windward side of the outdoor condenser 11 and configured to detect the outdoor ambient temperature. The indoor ambient temperature sensor 25 is arranged at a fin on the windward side of the indoor evaporator 12 and configured to detect the indoor ambient temperature. The evaporator middle-region temperature sensor 26 is arranged at a surface of a copper pipe located at a middle region of the indoor evaporator 12 and configured to detect a temperature of the middle region of the indoor evaporator 12.
The working principle of the air conditioner in embodiments of the present invention is as follows.

(1) When the air conditioner is in a cooling mode, the high-temperature and high-pressure gaseous coolant is discharged from the compressor 17, flows through the separator 22 and the four-way valve 20 and arrives at the outdoor condenser 11 for heat dissipation. The coolant then passes through the first electronic expansion valve 15 (the opening degree is in a maximum level at this time), flows through the heat dissipation coolant pipe 14 inside the electric control box 13, is throttled by the throttle valve 16, and thus forms a low-temperature and low-pressure coolant. The low-temperature and low-pressure coolant flows through the first coolant branch of the plate heat exchanger 19, enters the indoor evaporator 12 and is subjected to vaporization via heat absorption, followed by entering the liquid storage tank 21. The gaseous coolant flows into the compressor 17 for circulation.
(2) When the air conditioner is in a heating mode, the high-temperature and high-pressure gaseous coolant is discharged from the compressor 17, flows through the separator 22 and the four-way valve 20, and arrives at the indoor evaporator 12 and is subjected to heat dissipation. The coolant then flows into the first coolant branch of the plate heat exchanger 19 and flows to the throttle valve 16 (the coolant is not throttled at the time of heating), followed by passing through the heat dissipation coolant pipe 14 inside the electric control box 13, throttled via the first electronic expansion valve 15, thus forming a low-temperature and low-pressure coolant. The coolant flows into the outdoor condenser 11 for vaporization via heat absorption and enters the liquid storage tank 21. The gaseous coolant flows into the compressor 17 for circulation. The plate heat exchanger 19 is configured to, in the heating mode, realize heat exchange of coolants with different temperatures in the first coolant branch and the second coolant branch passing through the inside of plate heat exchanger 19, so as to make the coolant in the compressor air-injection enthalpy-increasing port 34 to be gaseous, thereby greatly increasing the heating capacity output of the compressor 17 under certain conditions.

According to the invention, the air conditioner further includes a controller.
According to the invention, the controller is configured to:

acquire an outdoor ambient temperature T4 after the air conditioner is turned on in the cooling mode,
acquire a preset current threshold I0, a preset compressor frequency threshold F0 and a preset current difference threshold A corresponding to the outdoor ambient temperature T4,
acquire, at the time that the compressor 17 is started for a first set time, a working current as a first current I1,
acquire, at the time that the compressor 17 is started for a second set time, a working current as a second current I2, and acquire, at the time that the compressor 17 is started for the second set time, a compressor frequency F,
control the air conditioner to stop and exchange control strategies for the first electronic expansion valve 15 and the second electronic expansion valve 18 when the following three conditions are met at the same time:
- the second current I2 being greater than the preset current threshold I0,
- a difference I2-I1 between the second current I2 and the first current I1 being greater than the preset current difference threshold A, and
- the compressor frequency F at the time that the compressor 17 is started for the second set time being less than the preset compressor frequency threshold F0.

In embodiments of the present disclosure, a mapping relationship between the outdoor ambient temperature T4 and the preset current threshold I0, the preset compressor frequency threshold F0 and the preset current difference threshold A can be pre-established in a program. After the air conditioner is turned on in the cooling mode, the outdoor ambient temperature T4 is acquired via the outdoor ambient temperature sensor 23 shown in Fig. 2. The above mapping relationship is queried to acquire the preset current threshold I0, the preset compressor frequency threshold F0 and the preset current difference threshold A corresponding to T4. A working current at the time that the compressor 17 is started for a first set time is acquired and used as a first current I1. A working current at the time that the compressor 17 is started for a second set time is acquired and used as a second current I2, and a compressor frequency F at the time that the compressor 17 is started for the second set time is acquired. When the following three conditions are met at the same time: I2>I0, I2-I1>A and F<F0, it is determined that the first electronic expansion valve 15 and the second electronic expansion valve 18 are plugged in reverse at the time, and thus the built-in preset program controls the air conditioner to stop and exchanges control strategies for the first electronic expansion valve 15 and the second electronic expansion valve 18. The control strategy refers to a control means on the opening degree of the first electronic expansion valve 15 and the second electronic expansion valve 18 in the cooling mode or the heating mode. If for example the control strategy for the first electronic expansion valve 15 is the first opening degree and the control strategy for the second electronic expansion valve 18 is the second opening degree at the time the three conditions are met in the cooling mode, the program exchanges the control strategy for the first electronic expansion valve 15 to the second opening degree and exchanges the control strategy for the second electronic expansion valve 18 to the first opening degree, thereby ensuring the normal operation of the air conditioner and improving system reliability.
According to the air conditioner proposed in embodiments of the present invention, the outdoor condenser is communicated with a first end of the heat dissipation coolant pipe via the first electronic expansion valve, the indoor evaporator is communicated with a second end of the heat dissipation coolant pipe via the throttle valve, and the heat dissipation coolant pipe is arranged in an electric control box. The heat dissipation coolant pipe is configured to dissipate heat from the electric control box of the air conditioner, thereby timely removing heat generated by the electric control box, lowering the element temperature, and improving the reliability and service life of the air conditioner. Further, the invention enables a variable frequency air conditioner to reach high operating frequencies and output high power under a high temperature, thereby displaying advantages of the variable frequency air conditioner and meeting user requirements. Furthermore, the air conditioner can be controlled to stop and control strategies for a first electronic expansion valve and a second electronic expansion valve can be exchanged when the following three conditions are met at the same time, so as to ensure that the air conditioner can still operate normally when the first electronic expansion valve and the second electronic expansion valve are plugged in reverse, thereby improving the system reliability, in which the three conditions are: the second current being greater than the preset current threshold, a difference between the second current and the first current being greater than the preset current difference threshold, and the compressor frequency at the time that the compressor is started for the second set time being less than the preset compressor frequency threshold.
Fig. 3 is a flow chart showing a control method for an air conditioner according to the present invention.
The control method is suitable for the air conditioner in embodiments of the above aspects.
As shown in Fig. 3, the control method includes the following steps.
S101 an outdoor ambient temperature is acquired after the air conditioner is turned on in a cooling mode.
S102 a preset current threshold, a preset compressor frequency threshold and a preset current difference threshold corresponding to the outdoor ambient temperature are acquired.
S103 a working current at the time that the compressor is started for a first set time is acquired as a first current.
S 104 a working current as a second current and a compressor frequency are acquired at the time that the compressor is started for the second set time.
S105 the air conditioner is controlled to stop and control strategies for a first electronic expansion valve and a second electronic expansion valve are exchanged when the following three conditions are met at the same time: the second current being greater than the preset current threshold, a difference between the second current and the first current being greater than the preset current difference threshold, and the compressor frequency at the time that the compressor is started for the second set time being less than the preset compressor frequency threshold.
It should be noted that the foregoing description on embodiments of the air conditioner is also applicable to the control method for the air conditioner in this embodiment, which is not repeated.
According to the control method for an air conditioner proposed in embodiments of the present invention, the outdoor condenser is communicated with a first end of the heat dissipation coolant pipe via the first electronic expansion valve, the indoor evaporator is communicated with a second end of the heat dissipation coolant pipe via a first coolant branch of the plate heat exchanger and the throttle valve in sequence, and the heat dissipation coolant pipe is arranged in an electric control box. The heat dissipation coolant pipe is configured to dissipate heat from the electric control box of the air conditioner, thereby timely removing heat generated by the electric control box, lowering the element temperature, and improving the reliability and service life of the air conditioner. Further, the invention enables a variable frequency air conditioner to reach high operating frequencies and output high power under a high temperature, thereby displaying advantages of the variable frequency air conditioner and meeting user requirements. Furthermore, the air conditioner can be controlled to stop and control strategies for a first electronic expansion valve and a second electronic expansion valve can be exchanged when the following three conditions are met at the same time, so as to ensure that the air conditioner can still operate normally when the first electronic expansion valve and the second electronic expansion valve are plugged in reverse, thereby improving the system reliability, in which the three conditions are: the second current being greater than the preset current threshold, a difference between the second current and the first current being greater than the preset current difference threshold, and the compressor frequency at the time that the compressor is started for the second set time being less than the preset compressor frequency threshold.
Fig. 4 is a schematic diagram illustrating structure of a control device for an air conditioner according to the present invention.
The control device for the air conditioner is suitable for the air conditioner in embodiments of the above aspects.
As shown in Fig. 4, the control device for the air conditioner includes:

a first acquiring module 41, configured to acquire an outdoor ambient temperature after the air conditioner is turned on in a cooling mode,
a second acquiring module 42, configured to acquire a preset current threshold, a preset compressor frequency threshold and a preset current difference threshold corresponding to the outdoor ambient temperature,
a third acquiring module 43, configured to acquire, at the time that the compressor is started for a first set time, a working current as a first current,
a fourth acquiring module 44, configured to acquire, at the time that the compressor is started for a second set time, a working current as a second current, and acquire, at the time that the compressor is started for the second set time, a compressor frequency, and
a first control module 45, configured to detect and confirm that the following three conditions are met at the same time, and control the air conditioner to stop and exchange control strategies for a first electronic expansion valve and a second electronic expansion valve, wherein the three conditions are:
- the second current being greater than the preset current threshold,
- a difference between the second current and the first current being greater than the preset current difference threshold, and
- the compressor frequency at the time that the compressor is started for the second set time being less than the preset compressor frequency threshold.

It should be noted that the foregoing description on embodiments of the air conditioner is also applicable to the control device for the air conditioner in this embodiment, which is not repeated.
According to the control device for the air conditioner proposed in embodiments of the present invention, the outdoor condenser is communicated with a first end of the heat dissipation coolant pipe via the first electronic expansion valve, the indoor evaporator is communicated with a second end of the heat dissipation coolant pipe via a first coolant branch of the plate heat exchanger and the throttle valve in sequence, and the heat dissipation coolant pipe is arranged in an electric control box. The heat dissipation coolant pipe is configured to dissipate heat from the electric control box of the air conditioner, thereby timely removing heat generated by the electric control box, lowering the element temperature, and improving the reliability and service life of the air conditioner. Further, the invention enables a variable frequency air conditioner to reach high operating frequencies and output high power under a high temperature, thereby displaying advantages of the variable frequency air conditioner and meeting user requirements. Furthermore, the air conditioner can be controlled to stop and control strategies for a first electronic expansion valve and a second electronic expansion valve can be exchanged when the following three conditions are met at the same time, so as to ensure that the air conditioner can still operate normally when the first electronic expansion valve and the second electronic expansion valve are plugged in reverse, thereby improving the system reliability, in which the three conditions are: the second current being greater than the preset current threshold, a difference between the second current and the first current being greater than the preset current difference threshold, and the compressor frequency at the time that the compressor is started for the second set time being less than the preset compressor frequency threshold.
It should be noted that the air conditioner may also work at a low temperature (for example, the outdoor ambient temperature is -10° C or below) during the actual operation. When the air conditioner works at the low temperature, the outdoor heat exchange is sufficient due to the very low outdoor ambient temperature, thereby the coolant after heat exchange in the outdoor side exhibits an excessive degree of supercooling, causing the coolant after throttling has a very low temperature. Thus, it is easy to trigger an indoor preset anti-freezing protection program, resulting in frequent shutdowns, which would not only cause large fluctuations in the indoor temperature, but also generate noise due to frequent startup and shutdown; at the same time, the excessive degree of supercooling results in that the coolant cannot vaporize completely when passing through the indoor side, generating the liquid compression in the compressor, which affects the reliability and service life of the compressor.
At present, the air conditioner is usually additionally equipped with temperature sensors or pressure switches or is disposed to change the heat dissipation area of some condensers to ensure the operation in a low temperature environment. However, these solutions not only lead to an increased cost, but also reduce the production efficiency and increase difficulty of after-sales maintenance. Based on the above, this present disclosure also proposes another control method for an air conditioner, which enables the air conditioner to operate stably and reliably at a low temperature, with a low cost, a high production efficiency and convenient for after-sales maintenance.

Claims

An air conditioner, comprising: an outdoor condenser (11), an indoor evaporator (12), a first electronic expansion valve (15), a throttle valve (16), and a heat dissipation coolant pipe (14) arranged in an electric control box (13), wherein
the outdoor condenser (11) is communicated with a first end of the heat dissipation coolant pipe (14) via the first electronic expansion valve (15),

the indoor evaporator (12) is communicated with a second end of the heat dissipation coolant pipe (14) via the throttle valve (16),

the first electronic expansion valve (15) is configured to throttle a coolant in a heating mode, and

the throttle valve (16) is configured to throttle the coolant in a cooling mode.

the air conditioner further comprising: a compressor (17), a second electronic expansion valve (18) and a plate heat exchanger (19), wherein

the indoor evaporator (12) is communicated with the throttle valve (16) via a first coolant branch of the plate heat exchanger (19),

the compressor (17) is communicated with the throttle valve (16) via a second coolant branch of the plate heat exchanger (19) and the second electronic expansion valve (18) in sequence, and

the second electronic expansion valve (18) is configured to throttle the coolant in a heating mode,

the air conditioner further comprising a controller, the air conditioner being characterised in that

the controller is a controller according to claim 5.
The air conditioner according to claim 1, further comprising a four-way valve (20) and a liquid storage tank (21), wherein
a first valve port of the four-way valve (20) is communicated with the outdoor condenser (11),

a second valve port of the four-way valve (20) is communicated with the indoor evaporator (12),

a third valve port of the four-way valve (20) is communicated with the liquid storage tank (21),

a fourth valve port of the four-way valve (20) is communicated with the compressor (17), and

the liquid storage tank (21) is communicated with the compressor (17).
The air conditioner according to claim 2, further comprising a separator (22), wherein
the liquid storage tank (21) and the compressor (17) are respectively communicated with the fourth valve port of the four-way valve (20) via the separator (22).
A control method for the air conditioner of claim 1, the control method comprising:
acquiring an outdoor ambient temperature when the air conditioner is turned on in a cooling mode,

acquiring a preset current threshold, a preset compressor frequency threshold and a preset current difference threshold corresponding to the outdoor ambient temperature,

acquiring, at the time that the compressor (17) is started for a first set time, a working current as a first current,

acquiring, at the time that the compressor (17) is started for a second set time, a working current as a second current, and acquiring, at the time that the compressor (17) is started for the second set time, a compressor frequency,

detecting and confirming that the following three conditions are met at the same time, and controlling the air conditioner to stop and exchanging control strategies for a first electronic expansion valve (15) and a second electronic expansion valve (18), wherein the three conditions are:
the second current being greater than the preset current threshold,

a difference between the second current and the first current being greater than the preset current difference threshold, and

the compressor frequency at the time that the compressor (17) is started for the second set time being less than the preset compressor frequency threshold.
A controller for an air conditioner, the controller comprising:
a first acquiring module (41), configured to acquire an outdoor ambient temperature after the air conditioner is turned on in a cooling mode,

a second acquiring module (42), configured to acquire a preset current threshold, a preset compressor frequency threshold and a preset current difference threshold corresponding to the outdoor ambient temperature,

a third acquiring module (43), configured to acquire, at the time that the compressor (17) is started for a first set time, a working current as a first current,

a fourth acquiring module (44), configured to acquire, at the time that the compressor (17) is started for a second set time, a working current as a second current, and acquire, at the time that the compressor (17) is started for the second set time, a compressor frequency, and

a first control module (45), configured to detect and confirm that the following three conditions are met at the same time, and control the air conditioner to stop and exchange control strategies for a first electronic expansion valve (15) and a second electronic expansion valve (18), wherein the three conditions are:
the second current being greater than the preset current threshold,

a difference between the second current and the first current being greater than the preset current difference threshold, and

the compressor frequency at the time that the compressor (17) is started for the second set time being less than the preset compressor frequency threshold.